In the electronic field, a higher packaging density has been desired for mounting electronic devices. Thus, attention has been paid to a technique of bonding already-packaged semiconductor integrated circuits (chips) onto a wafer (substrate) in a flip chip mounting manner. Chips have metal regions in a bump (projection) form or plate form. Electrical connection can be established through the metal regions between the chips and a wafer; or, in the case of laminating the chips three-dimensionally, between the laminated chips. In order to raise the mechanical strength of anyone of the chips, the chip may have a moiety to be bonded to the wafer or to different one of the chips. The moiety may be formed as one or more metal regions. By use of the metal region(s) to establish electrical connection and raise mechanical strength between the chips and the wafer or between the laminated chips, the transfer and reception of electrical signals can be made speedy between the chips and the wafer or between the laminated chips, and the packaging density in electronic-device-mounting can be made high.
For chip-bonding in the flip chip mounting manner, a method has been developed which makes use of non conductive resin (or non conductive paste, NCP). Chips are pushed into a layer of the NCP painted onto a surface of a substrate onto which the chips are to be bonded, so that metal regions of the chips are brought into contact with metal regions or other predetermined moieties of the upper of the substrate to pre-bond the chips to the substrate. Thereafter, the resultant structure is subjected to a predetermined heat treatment to attain main bonding. Thus, electrical connection is established and mechanical strength is raised between the chips and the wafer (substrate). The NCP is a material adopted generally, following the adoption of a lead-free technique for chip-on-wafer bonding. The NCP has a function of bonding or pre-fixing chips onto a substrate, and further the NCP is filled into a gap between the bonded chips and the wafer to raise mechanical strength between the chips and the wafer. Thus, the NCP is used as an under fill material for protecting the bond surface therebetween from the environment.
As a flip chip mounting manner using no NCP, a manner has been formed in which chips having bumps the respective tips of which are made of soldering material are bonded onto predetermined moieties of a substrate. In general, at the time of solder bonding, a flux is used to improve the solder in wettability. Thus, after the completion of the bonding, a process of removing residues of the flux is performed. However, the removal of the flux tends to be increased in difficulty with an increase in the packaging density in chip-mounting and a rise in the minuteness of microstructures of the bond surface.